1. Field of the Invention
The present invention is related to a structure of high efficiency solar cell, especially, to a high efficiency indium gallium phosphide NIP solar cell wherein an intrinsic layer between an emitter layer and base layer can suppress the Zu memory effect and interdiffusion and also a higher doping concentration in the n-type AlInP window layer can be attained and the lifetime of minority carriers also increase which improve the conversion efficiency.
2. Description of the Prior Art
The present invention is related to a high efficiency solar cell structure, especially, to a high efficiency indium gallium phosphide NIP solar cell wherein an intrinsic layer between a emitter layer and base layer can suppress the Zn memory effect and interdiffusion and also a higher doping concentration in the n-type AlInP window layer can be attained and the lifetime of minority carriers also increase which improve the conversion efficiency.
Nowadays, electric power may be generated from hydroelectricity, heat, fuel, nuclear and solar power, wherein the most important power generation method is solar power, because the equipment of solar power generation is the most compact and economic one, and since no fuel is needed so the environment will not be polluted.
In order to produce the energy supply in the 21st century and also considering the problem of environment protection, solar power is the most important and nowadays the key point about research of solar power is how to improve the conversion efficiency thereof. Now the highest efficiency of the solar cell is the tandem cell which is combined from GaInP/GaAs under the condition of AMO the efficiency of the tandem cell is about 30%. The principle thereof is to use two solar cells with two different absorption bands which are connected by a tunnel diode. The focus about the tandem cell is a GaInP solar cell in the upper layer thereof since the GaAs solar cell is a mature product either in experimental environment or in the commercial usage. In the prior art there are two structures about the GaInP:
(1) P/N type, that is, the P type is positioned atop the N type, the defect of which is that generally the window is made of indium gallium aluminum phosphide, but the highest concentration of P type dopant in this material is 5.times.10.sup.17 cm.sup.-3, thus it will increase the serial resistance and the light with short wavelength will be absorbed too much, therefore, the conversion efficiency of the solar cell may be reduced.
(2) N/P type, that is, the N type is positioned atop the P type, the trouble induced from this N/P type structure is that generally the P type dopant, zinc, has special memory effect, and could be decomposed through diffusion or by other growth material containing zinc to dope into the N type layer continuously so that the whole conversion efficiency is reduced.